Because they disallow inheritance, sealed classes are crucial to object-oriented design in C#. The compiler (and other developers) are informed that a class cannot be used as a base class when it is marked as sealed.
This is useful for,
- Enforcing design constraints.
- Improving performance (in some cases).
- Preventing misuse of certain classes.
What is a Sealed Class in C#?
A sealed class is a class that cannot be inherited. It is declared using the sealed keyword.
Trying to inherit from this class will result in a compile-time error:
When to Use Sealed Classes?
You might want to use sealed in these situations.
- To prevent unintended inheritance.
- To protect sensitive behavior from being overridden.
- To optimize performance in certain scenarios (because method calls to sealed classes can sometimes be optimized by the JIT compiler).
Example: Sealing a Class
Sealing a Method
You can also seal a method in a derived class to prevent further overriding. This only makes sense in a class that is already overriding a method from its base class.
Sealed Class vs Abstract Class
| Feature | Sealed Class | Abstract Class |
|---|---|---|
| Can be inherited | ❌ No | ✅ Yes |
| Can be instantiated | ✅ Yes | ❌ No |
| Use case | Lockdown behavior | Provide base functionality |
| Modifier | sealed | abstract |
Summary
- A sealed class in C# cannot be inherited.
- It’s useful for protecting class logic, improving performance, and enforcing strict designs.
- You can also seal methods in a class to prevent further overrides.
Keywords: sealed, inheritance, override, class design.
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